The present invention is directed to a hydraulic system for pressurizing a clutch having an emergency release mechanism, into which a device for increasing pressure is integrated in order to reduce the pedal force. Typically, such a pressure increase is produced by an electrical pump, which additionally increases the pressure between the master cylinder and the slave cylinder in the hydraulic system. This pump is electronically controlled by pressure sensors, for example, since the pump pressure is dependent on the pressure prevailing in the hydraulic system. However, when this pump or the electromotor experiences a failure, the clutch is not able to be actuated, not even in response to an increased expenditure of force. The reason for this lies in the structural design requirements of servo power assistance in normal operation.
From the related art, approaches are known for clutches that are actuatable by electromechanical actuators. In the event of a power failure in the drive system, for instance, the actuator remains in the currently active position, and the clutch can no longer be disengaged. To be able to nevertheless disengage the clutch in such a situation, an emergency release valve is employed between the master cylinder and the slave cylinder, to enable the hydraulic system to be manually or automatically disengaged. By opening the valve in this manner, the pressure in the reservoir is relieved and the engaged clutch is disengaged.
PCT Patent Application WO 2004/053348 A2 describes an approach for disengaging the clutch in the event that the elements required for clutch actuation fail. For example, if an element required for clutch actuation fails at a time when one or more clutches are engaged, an option is provided for disengaging the clutch or the clutches in order to tow the vehicle. This is accomplished, for example, by relieving the hydraulic system in that the pressure line is opened and thereby depressurized or in that the master cylinder is relieved.
In an approach for pressurizing the clutch using pedal force assistance, other components in the hydraulic system, such as the electromotor and the hydraulic pump, which are likewise no longer able to execute their function in the event of a power failure, also supervene. The result is that the clutch or, in the case of a twin clutch, both clutches are no longer able to be disengaged, not even in response to an increased expenditure of force.